The invention relates to a mobile crane comprising a main jib which is mounted in a luffable manner thereon and can be raised by means of a luffing cylinder, and comprising a main jib extension which is releasably connected to a main jib head of the main jib by means of upper and lower bolts, the main jib extension, proceeding from a basic position after release of the upper or lower bolts, can be angled relative to the main jib about a luffing axis by means of an angling drive, the angling drive engages a foot of the main jib extension, a maximum angling angle is limited by an adjustable angling plate and the angling plate engages the foot of the main jib extension and the main jib head.
The invention also relates to a method for angling a main jib extension relative to a main jib of a mobile crane.
The German utility model DE 20 2004 020 760 U1 already discloses a mobile crane comprising a main jib and a main jib extension which is fastened to its main jib head. The main jib extension can be luffed from a basic position, in which the main jib extension is oriented with its longitudinal direction in extension of the longitudinal direction of the main jib, to a 20° position and a 40° position. Typically, the main jib extension is releasably fastened to the main jib head by means of two lower bolts arranged in the region of bottom chords of the main jib extension and by means of two upper bolts arranged in the region of top chords of the main jib extension. In order to be able to luff the main jib extension out of the basic position about the lower two bolts serving as a luffing axis, in a first step the two upper bolts are withdrawn and in a second step the luffing of the main jib extension is effected by means of hydraulic luffing cylinders which engage the main jib head and the main jib extension. The two upper bolts are inserted and withdrawn in each case by means of a hydraulic bolting cylinder. In order to supply power to the luffing cylinders and the bolting cylinders, an autarkical hydraulic unit is arranged on the lower end of the main jib extension. The hydraulic unit used can be e.g. a diesel motor or electric motor each having an associated hydraulic pump.
German patent document DE 103 21 493 B4 discloses a mobile crane comprising a main jib extension and an angling plate. The angling plate is designed as a mechanically lockable telescopic apparatus having a tubular guiding plate and a sliding plate which is guided and extendible therein and is likewise tubular. The guiding plate has stop openings for receiving bolts which serve to support the sliding plate at its lower end and thus permit a preselected length of the angling plate and thus angular adjustment of the main jib extension. The angling plate is arranged in the region of a bottom chord of the main jib and the main jib extension. The desired angling is achieved by raising the main jib, whereby the angling plate is reduced in length until the sliding plate impinges upon the bolt and is supported thereon.
Moreover, European patent application EP 2 253 576 A1 discloses another embodiment of an angling plate for angling a main jib extension of mobile cranes. The angling plate which is formed from two angle levers has, in its basic position which corresponds to a 0° position of the main jib extension with respect to the main jib, several pairs of aligned stop openings for bolts. By selecting one pair of the stop openings for the bolts, the length of the angling plate can be varied and the main jib extension can be fixed in various angular positions, preferably 0°, 20° and 40°. The actual angular movement of the main jib extension is effected by means of a lifting machine located on the crane or next to the crane.